Can I assign Aruba Central license only to the master access point with in IAP cluster?
The master IAP (or) virtual-controller in the cluster is the one who communicates with management servers such as Aruba Central / Airwave.
IAP cluster architecture is designed to have redundant master in the IAP cluster, when the existing master goes down. The election process in the cluster, helps an other IAP to get elected as master. With this elected role , the new master initiates a connection with Central/Airwave.
Hence it becomes utmost important that all the IAPs in the cluster to be licensed and can communicate with central when elected as Master.